[m5k]

Looking for an open source CNC machine design. Would the MechMate (MechMate CNC Router - Build your own with our detailed plans) work for milling PCBs?

[ger21]

Just about any CNC will work. A mechmate is not ideal for that purpose, though.

[m5k]

Why is the Mechmate not ideal for this purpose?

[ger21]

1) It's 10x larger than you need.
2) It needs to be built very accurately to get the very precise Z axis depths you'll need.

The Mechmate was designed to cut full sheets of cabinet parts.
A small $500 Chinese machine from Ebay machine might do a better job with PCB's.

[blinkenlight]

I Agree.

Why is the Mechmate not ideal for this purpose?

Because (much like many other machines of similar size not meant for precision work) it seems to be rolling around on roller wheels as far as one can tell without having access to any actual information about the design. That may be fine for macro-level operations like plasma cutting or wood cutting where nobody cares about practical precision below a millimeter or so, but practical PCB milling requires far more precision than that. Making PCBs can give a tough time even to a machine on slide bearings. As a side note I'm also quite wary of "free" offers that nonetheless come with a long page of testimonials and a requirement to register for access - neither of which is of any use for offering something truly free of ulterior motive; then again, that's just me, and I'm known to be a cynical bastard.

[m5k]

The first point _sounds_ like a perk since you can use it for more than PCBs.
The second point is concerning. What is precision in this case? I imagine it isn't simply tightening bolts.

[blinkenlight]

There's any number of ways to quantify different aspects of what we colloquially just call "precision", but in this case the thing that gets you is the machine's ability to return to the exact same spot again and again and again. Specifically, how much it will err because no machine is absolutely precise. And great-sounding specs like how many separate "steps" the machine can ideally make within a single millimeter or other similar numbers will not help you any at this: all that matters is, if I physically stick a dial indicator to the frame, zero it out on the spindle, then send the machine around again and again, what error will it show when the spindle returns each time. And it needs to be small indeed, for PCB work, in each direction. Consider the typical feature size on the kind of PCB you intend to make, and you can make up your own mind about the precision you need - it will absolutely differ for a PCB with 0.5mm pin pitch integrated circuits or a PCB with large, trough-hole passive parts. There are also other, related precision concerns - such as runout on the spindle and collet you use, which can absolutely get you for really fine PCBs, but the main problem is typically repeatability...

[HPB]

You are spot on.

15 years ago I was dreaming of buying an LPKF CNC from Germany, I almost wasted my money.
Bought a ball screw CNC on Amazon for $600.

Cheers.